<!DOCTYPE html>
<html lang="en" xmlns:wicket>
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div.my-tree div.wicket-tree {
            height: 80em;
        }
    </style>
</head>
<body>
<a href="#" wicket:id="expandAll">expand</a>
<a href="#" wicket:id="collapseAll">collapse</a>

<div wicket:id="treeTable" class="my-tree"></div>
</body>
</html>